Process for hydrotreating heavy hydrocarbon feeds with switchable reactors including at least one step of progressive switching

Abstract

Process for hydrotreating a heavy hydrocarbon fraction using a system of switchable fixed bed guard zones each containing at least one catalyst bed including at least one step during which the flow of feed supplied to the first guard zone brought into contact with the feed is partly displaced to the next guard zone downstream, preferably progressively.

The invention claimed is: 
     
       1. A process for hydrotreating a heavy hydrocarbon fraction containing asphaltenes, sediments, sulphur-containing, nitrogen-containing and metallic impurities, said process comprising:
 passing a feed of said heavy hydrocarbon fraction and hydrogen, under hydrotreating conditions, over a hydrotreating catalyst, in at least two fixed bed hydrotreating guard zones, each guard zone containing at least one catalyst bed, said guard zones being arranged in series to be used cyclically, wherein said process comprises: 
 a) passing the feed through all the guard zones arranged in series during a fraction of the deactivation time and/or clogging time of the first guard zone of the series of guard zones that is brought into contact with the feed,
 a′) continuing to pass a portion of the feed through the first guard zone that is brought into contact with the feed while introducing another portion of the feed into the next guard zone downstream of the first guard zone in the series of guard zones for a period at most equal to the deactivation time and/or clogging time of the first guard zone that is brought into contact with the feed, 
 b) by-passing the first guard zone which is deactivated and/or clogged and regenerating and/or replacing with fresh catalyst the catalyst in the deactivated and/or clogged first guard zone while continuing to pass the feed through the other guard zone(s) in the series of guard zones, 
 c) passing the feed through all the guard zones in the series of guard zones, during which the guard zone in which the catalyst was regenerated during the preceding step is reconnected to the series of guard zones so as to be downstream of all the other guard zones, and continuing to pass the feed through all the guard zones in the series of guard zones for a fraction of the deactivation time and/or clogging time of the first guard zone in the series of guard zones that is brought into contact with the feed, 
 c′) continuing to pass a portion of the feed through the first guard zone in the series of guard zones that is brought into contact with the feed while introducing another portion of the feed into the next guard zone downstream of the first guard zone in the series of guard zones for a period at most equal to the deactivation time and/or clogging time of the first guard zone that is brought into contact with the feed, and 
 
 successively repeating b), c) and c′). 
 
     
     
       2. The process according to  claim 1 , wherein during a′) and c′) said portion of the feed introduced into the next guard zone downstream does not exceed 50% of the total feed. 
     
     
       3. The process according to  claim 1 , wherein during a′) and c′) said portion of the feed introduced into the next guard zone downstream increases progressively. 
     
     
       4. The process according to  claim 3 , wherein the progressive increase is carried out continuously or in stages. 
     
     
       5. The process according to  claim 3 , wherein the increase in the portion of the feed introduced into the next guard zone downstream is from 0.02 to 4% per % of the deactivation time and/or clogging time. 
     
     
       6. The process according to  claim 3 , wherein the increase in the portion of the feed introduced into the next guard zone downstream is from 0.02 to 1% per % of the deactivation time and/or clogging time. 
     
     
       7. The process according to  claim 1 , wherein a) and c) are carried out for a period between 30 and 95% of the deactivation time and/or clogging time of the first guard zone brought into contact with the feed. 
     
     
       8. The process according to  claim 1 , wherein a) and c) are carried out for a period between 60 and 90% of the deactivation time and/or clogging time of the first guard zone brought into contact with the feed. 
     
     
       9. The process according to  claim 1 , wherein said another portion of the feed introduced at the beginning of a′) and c′) into the next guard zone downstream of the first guard zone in the series of guard zones is from 0 to 50% of the total feed, expressed in vol. %. 
     
     
       10. The process according to  claim 1 , wherein said another portion of the feed introduced at the beginning of a′) and c′) into the next guard zone downstream of the first guard zone in the series of guard zones is from 20 to 40% of the total feed, expressed in vol. %. 
     
     
       11. The process according to  claim 1 , wherein the degree of hydrotreating is maintained by raising the temperature. 
     
     
       12. The process according to  claim 1 , wherein, at the entrance of each guard zone, the feed passes through a filtering distributor plate composed of a single stage or of two successive stages, said plate being situated upstream of the catalyst bed(s). 
     
     
       13. The process according to  claim 1 , wherein said process precedes a fixed bed or ebullating bed hydrotreating process.